I'm so sorry your kiddo is going thru these tough health problems
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First and most importantly, are you actually seeing a Vet Internist for these issues - they would be your *best* source of reliable information....?
Here are the product ingredients: A Proprietary Blend of Rehmannia Root (Rehmannia Glutinosa), Cultivated Cordyceps Mycelium (Cordyceps Sinensis), Astragalus Root (Astragalus Membranaceus), Dong Quai Root (Angelica Sinesis).
So, it's an herbal blend, basically. While herbs - especially "herbal tonics" certainly can have positive effects on humans and animals -- I'm not sure this is where you should be focusing at present, honestly.
You mentioned he "may have liver cancer" -- liver cancer tends to be fatal relatively quickly -- so what's happening w/ liver values...do you know...? I think I'd be focusing there, personally.
If I were you, I'd get my kiddo to an Internist to discuss liver/kidneys -- and I'd print out info regarding this product -- bring it to the appointment.